1. Field of the Invention
The present invention relates to object based graphics systems, and, in particular, discloses a method and apparatus for providing hidden surface removal by filling an object based rasterised image prior to displaying that image either on a video display or by means of printing.
2. Description of the Related Art
Most object based graphics systems utilise a frame store or page buffer to hold a pixel based image of the page or screen. The outlines of the objects are calculated, filled and written into the frame store. For two-dimensional graphics, objects which appear in front of other objects are simply written into the frame store after the background object, thereby replacing the background on a pixel-by-pixel basis. This is commonly known in the art as "Painter's algorithm". Images are calculated in object order, from the rearmost object to the foremost object. However, real-time image generation for raster displays requires the calculation of images in raster order. This means that each scan-line must be calculated as it is reached, thus requiring that the intersection points of each scan line with each object outline are calculated and then subsequently filled.
Although it is possible, with a line buffer rather than a page buffer, to use the Painter's algorithm within a scan-line to fill the objects, image generation in real-time, at video data rates is expensive using this method.